Despite providing the highest energy density commercially available, current Li-ion rechargeable battery technology still falls short of the desired energy, power and cost requirements of new applications such as electric vehicles (EV/PHEV's), electric bikes and scooters, web-enabled cell phones, and other advanced portable power applications. The use of very high capacity advanced negative electrode materials based on materials such as silicon and silicon carbon composite become more interested in achieving high energy density Li-ion cells. However, except its very high-volume expansion during charging and discharging, the silicon or silicon base negative electrode materials is suffered high irreversible capacity loss, too. There is a number of strategies for overcoming the high irreversible loss of silicon base anode, such as pre-lithiation of negative electrode material, providing extra lithium into a lithium ion cell apart from the positive electrode active material, etc. Battery systems that provide electrochemical energy conversion and storage are a practical solution to multiple energy generation applications, and a viable economic alternative to fossil fuel use. While rechargeable lithium-ion batteries provide the highest energy densities of commercial battery systems, the power generated does not currently meet the requirements of large scale electric vehicle and electric grid storage applications. New cell materials and lithium-ion cell technologies are needed to achieve greater energy densities.
The focus on new material development for lithium-ion batteries has been limited to materials compatible with assembling the lithium-ion cell in the discharged state, as is the current convention. This approach does provide significant benefits since active materials in the discharged state are stable and safely handled during cell manufacturing processes. Importantly, handling of lithium metal or highly reactive lithiated negative electrode materials is avoided, reducing manufacturing costs and increasing safety. The major disadvantage in utilizing discharged cell materials to construct lithium-ion cells is that the lithium available for cycling is derived solely from the active material of the positive electrode, which has a relatively low energy density, in the 140 mAh/g to 180 mAh/g range for materials currently used in conventional lithium-ion batteries. Additionally, such low energy density, discharged positive electrode materials limit the choice of negative electrode materials to those with small irreversible capacities because the negative electrode consumes lithium directly from the low energy density positive electrode active material. Without the limitation of such low energy density discharged positive electrode materials, the use of very high capacity negative electrode materials, such as silicon and tin would become practical. This would enable the production of higher energy density lithium-ion battery systems than are currently commercially available.
Several promising lithium-ion intercalating positive electrode materials that exist in the charged state could provide significant energy density increases if a source of lithium is provided in addition to the positive electrode active material. These intercalating materials include vanadium oxides such as V2O5 and LiV3O8, with theoretical capacities in the range of 300 mAh/g to 400 mAh/g; manganese oxides such as MnO2 with capacities exceeding 300 mAh/g. The vanadium oxide materials seemed promising because of their long cycle life, small voltage window, high capacity at moderately low voltage, low cost and safety. Unfortunately, the one battery system developed using vanadium oxide positive electrode materials proved to be impossible to manufacture in a commercially viable manner, due to safety issues that could not be resolved.
Strategies for providing additional lithium, not derived from the positive or negative electrode active materials, into a lithium-ion cell have been explored. Key requirements for such methods are, first, that the lithium source materials have a high effective lithium capacity so as not to negatively impact the cell energy density, and, second, that the lithium source material be sufficiently stable to be safely incorporated into the cell. To date such strategies have focused on the negative electrode as the lithium source material, and have involved handling of highly reactive lithiated materials or sacrificial lithium electrodes that have had negative impacts on manufacturing cost, safety and cell yield, or have required radical new cell designs and manufacturing processes, making them commercially infeasible.